Geology and geochronology of the super-large Bailongshan Li–Rb–(Be) rare-metal pegmatite deposit, West Kunlun orogenic belt, NW China

Abstract

The Bailongshan pegmatite deposit is a newly discovered super-large Li–Rb–(Be–Ta–Nb) rare-metal deposit in the West Kunlun orogenic belt, northwest China. Fifty-two rare-metal orebodies (50–1230 m long by 1.5–157 m wide) have been discovered by detailed field surveying, making up a metallogenic field that is larger than 8250 × 400 m. The deposit is estimated to have ore reserves of more than 5.06 million tonnes (t) Li2O, 160,020 t BeO, 316,200 t Rb2O, 40,060 t Nb2O5, and 10,750 t Ta2O5. Pegmatite dikes are zoned around a granodiorite batholith, ranging from barren through orebodies rich in Be, Nb, Ta, Rb, and Li with increasing distance from the batholith, similar to the classical model of a zoned Li–Ce–Ta (LCT)-type pegmatite. LA–ICP–MS analyses of coltan and zircon yield 206Pb/238U ages of 208.1 Ma and 212.3 Ma, respectively, representing the emplacement ages of the pegmatites and granodiorite. These data indicate a temporal link between the emplacement of the granodiorite batholith and rare-metal mineralization in the pegmatites, and that the Bailongshan rare-metal pegmatites are temporospatially related to the granodiorite batholith. The Bailongshan pegmatites and other rare-metal pegmatite deposits in the West Kunlun orogenic belt likely make up a >600-km-long Li metallogenic belt, and further exploration for rare-metal pegmatites should be focused on the area adjacent to Late Triassic granitoid plutons in the belt. This belt likely extends to the East Kunlun and West Sichuan rare-metal belts, forming the >2000-km-long, Late Triassic West Kunlun–Songpan–Garzê rare-metal metallogenic belt.